1. Field of the Invention
The present invention generally relates to focusing and aligning one or more laser beams, especially for use in a color image projection system in which laser beams of different wavelengths are used for projecting a two-dimensional image in color on a viewing surface away from the system.
2. Description of the Related Art
It is generally known to project a two-dimensional image on a screen based on a pair of scan mirrors which oscillate in mutually orthogonal directions to scan a laser beam over a raster pattern. However, the known image projection systems project the image with limited resolution, typically less than a fourth of video-graphics-array (VGA) quality of 640×480 pixels, and not in true color.
To obtain a true color image, red, blue and green laser beams emitted by lasers are needed. The wavelengths of such beams are extremely small. For example, a red laser beam has a wavelength on the order of 635-655 nanometers, and a blue laser beam has a wavelength on the order of 430-505 nanometers. These very short wavelength beams must be focused by focusing lenses to a very high degree of accuracy to collect practically all the energy emitted by the lasers and to prevent blurring and aberrations in the projected image. Each focusing lens has a mechanical or centration axis which must be precisely aligned to coincide with the optical axis along which the respective laser beam is directed. Experience has shown that the necessary centration accuracy is too difficult and too expensive to achieve by current precision manufacturing and assembly techniques so that unacceptable pointing errors between the centration axis and the optical axis for each beam unavoidably occur, thereby degrading the projected image.